The present invention relates generally to an apparatus for the distraction of bone or bone segments.
In modern surgical operative technique, external or also internal distractors are used to bring about a controlled displacement of bone fragments relative to one another. Endo-distractors are especially suitable for oral surgery, as they allow to minimize the disturbance of the patient during the distraction process which may often take several weeks.
Distractors are also used with toothless jaws in cases of advanced atrophy of the mandible. Apart from the cosmetic aspect, mandibular atrophy may also create difficulties for the implantation of a set of artificial teeth. The absence of the necessary bone substance may lead to a loosening of the implants or even to a fracture of the mandible. A pathological atrophy of the mandible is not only observed with old patients but may even occur with a 40-year-old patient, in which case the decision in favor of an operative intervention is greatly facilitated.
In order to rebuild the mandible, an osteotomy of the mandible is realized in a horizontal direction. Subsequently, the osteotomy gap is continuously increased. This distraction of the osteotomy gap is carried out at a rate on the order of about xc2xd mm per day. During the slowly advancing process of distraction, osseous tissue is formed in the osteotomy gap. After completion of the distraction, the osteotomy gap has to be maintained at the right distance for a certain period of time.
The present invention is directed to a device for the distraction of bones or bone segments comprising an anchoring screw having a longitudinal axis, a threaded shank, a screw shank, and a screw end provided with means for rotatably driving the anchoring screw, as well as a distraction sleeve axially displaceable along the screw shaft extending coaxially along the longitudinal axis and is provided with a rear end, a front end, a circular cylindrical, through-bore, an external screw thread adjoining the front end, and a coupling means formed on the rear end for receiving a driving tool. In addition, the anchoring screw comprises a collar located between the threaded shank and the non-threaded shank and projecting radially at least over the non-threaded shank so as to serve as an axial stop for the front end of the distraction sleeve that is slid over the screw shank. The through-bore comprises a boring section with an enlarged cross-section in which a seal ring is coaxially arranged between the lateral surface of the boring section and the screw shank.
In one embodiment of the device, the collar is shaped in the form of a cone which leads to the screw shaft. Thus, the contact surface between said cone and the front end of the distraction sleeve is minimized, which has the advantageous result that in spite of the axial load existing between the anchoring screw and the distraction sleeve, the anchoring screw remains easily rotatable about the longitudinal axis. Alternatively, the transition segment may also be spherically convex.
The device according to the invention comprises in addition, a cover screw which may be screwed into a bore formed on the screw end and provided with an internal screw thread. The cover screw forms the mechanical seal of the distractor in the oral cavity and, in addition, secures the anchoring screw in its position relative to the distraction sleeve.
In another embodiment, the collar comprises a spherically convex, tapered portion which leads to the screw shank. Also, the boring section can have an inner cone which leads to the through-bore. In another embodiment, the screw thread may be self-tapping, or the screw thread can have an asymmetrical thread profile. Also, the screw thread may include flanks directed towards the screw tip that form an angle of between 80 and 90 degrees with respect to the longitudinal axis.
Also, the external thread may have an asymmetrical thread profile, and the external thread may include flanks directed towards the rear end that form an angle of between 80 and 90 degrees with respect to the longitudinal axis, and the thread profile of the external thread may have flattened, threaded tips. In one embodiment, the means for rotatably driving the anchoring screw do not radially protrude from the screw shank.